Yeah, they could bump up the scale as Toho did 50+ years ago, but there are some problems with that. One, if you re-read what I said, there'd be an IP/legal issue getting in the way. I'd add to that by saying that this isn't the same as what Uni/Toho did - those were two movie studios from different countries which had no toes to step on. Uni and WB are both 'Murikan, and therefore are fighting for the same turf. I don't see it happening. Legally, the only way it could happen is if two things happen: 1) Godzilla is ripped out of the taloned fingers of WB and brought to Universal; and 2) if Toho thinks it would be a sane idea. I don't see it as even a slim chance.
Secondly, I'm among those that DOESN'T want to see this happen because you'd have to Nolan-ize Kong, or totally camp-out Godzilla and make him a comicbook-y luchador again. How will they make a 300+ foot tall ape even work? Does anyone want to see Ken Watanabe, with a straight face say something as silly as, "Yes, we had distant simian ancestors that no one knew about that averaged 250' to 350' tall…"? It'll delegitimize the whole endeavor.
I enjoyed Kong vs Godzilla when I was a child, when stuff like this didn't have to make sense. I also appreciate that the new Godzilla has matured and become super-serious once more so that I can enjoy it as an adult. However, I wouldn't appreciate an attempt at dark-campiness to make Kong a viable opponent in a future Godzilla film. I like pizza and I like chocolate cake, but I don't want chocolate cake on my pizza.